1. Field of the Invention
The present invention relates to a large relative aperture telecentric lens and, more particularly, to a projection lens adapted for use in a liquid crystal projector or the like.
2. Description of Related Art
In projection lenses for projecting an original image generated on a liquid crystal display or a cathode ray tube onto a screen in enlarged scale, there have been proposed a wide variety of projection lenses for use with the cathode ray tube, which are as fast as 1.5 or less in F-number. Concerning a projection lens for use in the three-tube type cathode ray tube projector, mention may be made of the proposals in, for example, Japanese Laid-Open Patent Application No. Hei 4-311910.
In the conventional projection lens described above, however, since a concave lens for correcting field curvature is disposed near the image plane, telecentricity is poor. Therefore, the above conventional projection lens cannot be used as a projection lens for use with the liquid crystal display, in which contrast varies to large extent depending on the angle of incidence of light. Also, in the above conventional projection lens, the corner illumination is as low as 35% or thereabout, and, therefore, a problem arises in that the projected image becomes dark in the marginal zone.
Accordingly, there have been few proposals made for a projection lens which is as fast as 1.5 or thereabout in F-number and still has a good telecentric property with the corner illumination increased so greatly that it is even applicable to the liquid crystal projector.